CX3C motif chemokine receptor 1 (CX3CR1), also known as the fractalkine receptor or G-protein coupled receptor 13 (GPR13), is a transmembrane protein of the G protein-coupled receptor 1 (GPCR1) family and the only known member of the CX3C chemokine receptor subfamily.[5][6][7]
As the name suggests, this receptor binds the inflammatory chemokineCX3CL1 (also called neurotactin in mice or fractalkine in humans). This endogenous ligand solely binds to CX3CR1 receptor. Interaction of CX3CR1 with CX3CL1 can mediate migration, adhesion and retention of leukocytes, because Fractalkine exists as membrane-anchored protein (mCX3CL1) as well as cleaved soluble molecule (sCX3CL1) due to proteolysis by metalloproteinases (MPPs). The shedded form carries out typical function of conventional chemokines, the chemotaxis, while the membrane-bound protein behaves as adhesion molecule for facilitation of diapedesis.[7][8]
Both partners of CX3CL1-CX3CR1 axis are present on numerous cell types from hematopoietic and nonhematopoietic cells throughout the body. Moreover, their distinct cell expression is dependent on specific tissues and organs, which provides broad sphere of biological activity. Hence, considering their various functional activity, they are also linked with multiple neurodegenerative and inflammatory disorders as well as with tumorigenesis.[7][8][9]